Shigella is a family of gram-negative bacteria that cause severe infections of the colonic epithelium, leading to an estimated 1.1 million deaths annually. After bacterial entry into host cells, the assembly of host actin into an actin tail at the bacterial pole is required for bacterial motility and spread. IcsA is a Shigella specific protein that is required for actin tail formation and is localized to the bacterial pole. IcsA is a member of the autotransporter family of secreted proteins;we have shown that autotransporters are generally secreted at the pole. The mechanism of localization of these proteins to the bacterial pole is highly conserved, but is as yet unidentified. My specific aims are: 1) to identify essential proteins required for localization of the autotransporter IcsA to the bacterial pole;2) to characterize the mechanism by which proteins identified in Aim 1 contribute to the localization of IcsA to the pole and the function of IcsA polarity in Shigella pathogenesis;and, 3) to define the role of the polar targeting machinery identified in Aims 1 and 2 in localizing other members of the autotransporter family and other polar proteins in Gram-negative bacteria. These approaches are highly likely to uncover components of the machinery that is required for localization of IcsA to the bacterial pole. This machinery is likely to be conserved among a broad range of Gram-negative bacteria and, because of its conservation, is likely to represent a general mechanism for the localization of a subset of polar proteins to the poles. Since many autotransporters are involved in virulence, elucidation of the mechanism of their localization to the pole may lead to the development of novel broad-spectrum antibiotics. PUBLIC HEALTH RELEVANCE: Infections by Shigella cause 1.1 million deaths annually, and create a severe monetary burden on underdeveloped nations. A more thorough understanding of proper virulence factor localization in these bacteria could lead to the development of novel broad-spectrum antibiotics. I propose a large scale analysis of S. flexneri proteins necessary for proper IcsA location, and subsequent intercellular spread during bacterial infection.